1. Field of the Invention
This invention relates to a detector device in which a mixing ratio of such as, for example, gasoline and alcohol is optically measured, and particularly concerned to the detector device suited for use in fuel of internal combustion engine.
2. Description of the Prior Art
In an internal combustion engine for motor vehicle, it has been suggested that mixing liquid of gasoline and alcohol would be applied to as a combustible fuel. When the liquid fuel is applied to as this combustible fuel it is necessary to continuously detect mixing liquid ratio of alcohol and gasoline so that an automatic combustion control unit may work to insure the most appropriate quantity of fuel injection in order to obtain an optimum output of the engine.
For this purpose, a detector device is provided which includes an optically permeable column. A circumferential surface of the column is immersed in mixing liquid of gasoline and alcohol.
Light beams of a light source enter from one end of the column to be incident on the circumferential surface of the column at an angle more than critical angle, and totally reflect at the circumferential surface. The totally reflected light beams emerge from the other end of the column to impinge on a photo diode which produces an output in accordance with an intensity of the light beams impinged on.
The theory is such that the critical angle changes depending upon the mixing degree of the mixing liquid, measuring the output form the photo diode enables to obtain the mixing liquid ratio.
In this device, however, the light source and the photo diode are axially located at both sides of the column, thus requiring two cases to discretely enclose the light source and the diode to add the number of assembly process.
In addition, axially dimension of the prior device inevitably become greater to render difficult to make a whole structure compact.
Therefore, it is an object of this invention to provide the detector device which is capable of making the optically permeable column compact, and contributing to cost-saving and reduction of assembly processes.
It is another object of this invention to provide the detector device which is capable of directing only required quantity of light beams to the photo diode, thus enabling to measure the mixing ratio of the mixing liquid with high accuracy.
According to this invention, there is provided a detector device comprising; the optically permeable column, one end which is coated with a light-reflective layer, at least the circumferential surface of said column being partially immersed in the mixing liquid of, such as, gasoline and alcohol or the like; a light emitting diode and photo diode each placed at opposite side to the light-reflective layer to align along a diametrical direction of the column; light beams from the light emitting diode forming such a light path that the light beams pass the column to be incident on the circumferential surface of said column and reflect form the circumferential surface to be incident on the light reflective-layer to reflect therefrom to impinge on the photo diode, the light beams incident on the circumferential surface of the column at less than the critical angle being refracted to said mixing liquid while the light beams incident on the circumferential surface at more than the critical angle being totally reflected, the critical angle depending on a mixing degree of the mixing liquid; and a diametrical and lengthwise dimension of the column being determined such as to provide incidence angles of the reflected light beams changing from a minimum angle corresponding to the critical angle when the mixing liquid ratio is at the lower limit of the predetermined range to a maximum angle corresponding to the critical angle when the mixing liquid ratio is at the upper limit of the predetermined range.